Using the honey bee as a model system to study the evolution of opportunistic pathogens

Opportunistic pathogens (OPs) are typically characterized as organisms that can only become pathogenic in susceptible hosts, e.g. hosts with weakened immune systems or altered microbiome composition. However, most of the time they can coexist rather peacefully within their host and can live in several non-host environments. It is possible that the virulence of OPs can evolve by “coincidental” selection because many functional virulence traits are more beneficial for competition outside the host environment. We are interested in understanding which selective forces drive the evolution of virulence in OPs. To address this we study Serratia marcescens, an OP of many animals including honey bees and other insects. Our aim is to determine what factors contribute to pathogenicity, how within host evolution impacts virulence, and how the native host microbial community responds to S. marcescens invasion, i.e. can the microbiome protect its host against infection. Here we demonstrate that the honey bee is a great model system to address these important questions.